Oil- or gas-heated burners have been used in Denmark for a rather long time for controlling Hylotrupes bajulus in roofs. Oil or gas is burned and the heat released in the process heats air, which is introduced with the combustion gases into the infested roof truss. After a correspondingly long exposure time, the pests in the rafters are dead. Similar processes are also used to control termites and cockroaches in the U.S.A. The buildings are wrapped in foils or tarpaulins at the same time in this process in order to keep the heat loss as low as possible. The wrapping of the buildings in tent foils is not possible or too expensive in the case of large objects, such as mills or large food-processing plants.
WO 92/00173 describes a process from the Netherlands, in which the heated air in the room being treated is additionally maintained at a minimum humidity level. The combustion gases are disadvantageously introduced into the room being treated; this process cannot be used in food-processing plants.
EP 0 416 255 A1 describes a process in which a mill, which is infested with pests, is freed from pests such that the inner walls are heated to a minimum temperature of about 27.degree. C. before carbon dioxide is admitted. For heating, heating devices are set up in the room to be treated itself, and the carbon dioxide is heated as well.
A thermal disinfestation process, in which explosion-proof electric heaters set up in the room to be treated are used, is described in the article by H. Hofmeier, Pest Control with Heat in Mills, Bakeries and Restaurants, Die Muhle+Mischfuttertechnik, Vol. 133, Nos. 51/52, Dec. 19, 1996, pp. 842 ff. The energy consumption is very high due to the relatively low efficiency of the electric heater, and mills with large room space can be heated up for pest control only if a block-type thermal power station is additionally available.
Electric heaters for pest control in mills, etc., are also described in the utility model DE 29618646 U1.
The article by J. A. Teich, Thermal Pest Control in Mills, Die Muhle+Mischfuttertechnik, Vol. 133, No. 11, Mar. 14, 1996, pp. 172 ff., describes a process in which hot steam is used for disinfection in mills. However, the hot steam may precipitate on cooler parts and damage due to moisture may thus occur in the mill. In addition, molds will increasingly grow after the heat treatment because of the increased moisture content present in the mill after the treatment.
Combinations of heat with carbon dioxide, phosphine and dichlorvos have become known from the U.S.A. U.S. Pat. No. 5,403,597 describes a combined process comprising heat from steam, natural gas and electricity, carbon dioxide and phosphine. Electric heaters are used predominantly. The electric heaters consume a very large amount of energy, and they are therefore sometimes replaced with gas-heated furnaces. These are operated until shortly before the admission of carbon dioxide and phosphine and are then switched off, because phosphine would decompose in the gas-heated burner. The consequence would be even more intense corrosion phenomena than those induced by phosphine itself. In addition, this process has the drawback that the room to be treated cools more or less rapidly during the gas exposure time after the gas-heated burners have been switched off (Fumigation and Pheromones Workshop, West Lafayette, Ind., U.S.A., 1996, with practical demonstration of the process by D. and J. Mueller). This leads to a loss of effectiveness during the process, because the pests breath in the phosphine substantially more rapidly at higher temperatures.
Problems also occur in the case of the use of carbon dioxide as a fumigant with the simultaneous heating of the atmosphere in the room being treated by means of oil- or gas-heated burners. Flue gases, which may contaminate the food remnants or foods proper in the room being treated, are generated by the combustion process. In particular, fuel oil contains sulfur compounds, which can be found in the form of sulfate or sulfite in food remnants in the mill. An overpressure is also generated in the room being treated due to the combustion process, because additional gases are introduced into the room being treated, so that the sealing needed for the fumigation may be damaged and greater losses of gas or heat may occur.